<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <title>Document</title>
</head>
<body>
  <ul id="myList"><li>苹果</li><li>橙子</li><li>橘子</li></ul>
  <ul id="op"></ul>
  <button>点我</button>
  <script>
    var btn = document.querySelector('button');
    btn.onclick = function () {
      var item = document.getElementById('myList').firstChild;
      var cloneItem = item.cloneNode(true);
      document.getElementById('op').appendChild(cloneItem);
    };
  </script>
</body>
</html>